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Abstract: The use of purified enzymes in microbial influenced corrosion (MIC) studies is increasingly recognized as a powerful tool to understand electrochemical interfacial processes, especially the ennoblement of stainless steels (SS) in natural waters. The ennoblement has attracted the interest of many researchers as the consequences in terms of pitting corrosion are still not well understood. In the present study, the ennoblement of AISI 316L SS was induced by glucose oxidase (Gox) catalyzed reaction or by adding hydrogen peroxide (H2O2) in synthetic fresh water, on the basis of previous work. The corrosion behavior of the sample was studied using potentiodynamic and galvanostatic polarization tests. When the ennoblement occurs, the pitting potential (E p) becomes nobler as well. The involvement of H2O2 to enhance pits repassivation seems to be a key consideration in this respect. Results obtained using this enzymatic system enable us to reappraise the commonly acknowledged hypothesis that the ennoblement increases the risk of localized attacks. [Copyright &y& Elsevier]

Abstract: In non-sterile aqueous media, stainless steels (SS) may exhibit a non-stable behavior resulting from interactions between microbial species and passive film. They can induce the increase of the Open Circuit Potential (OCP) and they do so when they are organized in biofilms. Numerous studies have reported the catalytic effect of biofilms, involving enzymes, and their influence on the local physicochemical conditions related to their heterogeneous structure. To date, there are no enzymatic models able to mimic the interfacial processes: generation of oxidant species and specific physicochemical conditions. In our study, a SS-modified electrode based on a classical enzyme immobilization technique was conceived. Glucose oxidase (Gox) was immobilized in a polymeric film poured on SS surface to concentrate the enzymatic activity near the metal/polymer film interface. Electrochemical tests were performed to compare the effect of Gox when immobilized or free in the electrolyte. These experiments provided fine details about the reduction of both oxidants involved in the Gox-catalyzed reaction: H2O2 and O2. The cathodic processes presented major differences between free and immobilized enzyme whereas the OCP ennoblement was found to be mainly due to an electrochemical effect of H2O2 in both cases. The immobilized Gox provoked a strong depletion of oxygen near the metal/polymer interface, indicating that the reduction current recorded was principally due to the H2O2 reduction. [Copyright &y& Elsevier]

The Fe(II–III) hydroxycarbonate green rust, GR(CO 3 2− ), can be prepared by oxidation of aerated aqueous suspensions of Fe(II) hydroxide. The effects of nitrite ions on the formation and oxidation of GR(CO 3 2− ) were then studied by adding NaNO 2 just after the precipitation of Fe(OH) 2 or once GR(CO 3 2− ) was obtained. The oxidation products were characterized by X-ray diffraction and Raman spectroscopy. In aerated conditions the oxidation of GR(CO 3 2− ) in the presence of nitrite species (0.004 to 0.1 mol L −1 ) is mainly due to dissolved O 2 . Nitrite however influences the transformation of GR(CO 3 2− ), promoting lepidocrocite at the detriment of goethite at 0.02 mol L −1 and hindering the crystallization of lepidocrocite at 0.1 mol L −1 . In anoxic conditions GR(CO 3 2− ) transforms spontaneously into a mixture of magnetite, siderite and chukanovite whether nitrite species are present or not. The proportion of magnetite is larger with nitrite which can be attributed to a partial reduction of NO 2 − by GR(CO 3 2− ). Finally, nitrite ions are able to oxidize rapidly Fe(OH) 2 into GR(CO 3 2− ) even in the presence of O 2 . With a sufficient nitrite concentration, the formation of GR(CO 3 2− ) is entirely due to nitrite reduction. [ABSTRACT FROM AUTHOR]

Abstract: Surface treatments and coatings are the practical approaches used to extend the lifetime of components and structures especially when the surface is the most solicited part of the considered engineering component. Hard thermally sprayed coating is one of the most wear resistance coating widely used in many practical mechanical applications. In the construction of articulating parts of medical devices, titanium and its alloys have to be surface coated to improve their tribocorrosion behavior. In this way, the use of porous thermal coatings is known to be a strategy for better binding bone or tissue on femoral stem for example. It is, thus, important to evaluate the corrosion and the wear behaviors of such materials for biosecurity considerations in the human body. In this study, we investigate the behavior of new nano ZrO2 and Al2O3-13wt.% TiO2 thermal sprayed coatings on commercially pure (cp)-Ti (grade 4) and titanium alloy substrates. Friction and wear tests against Al2O3 balls showed that the wear resistance of Al2O3-13wt.% TiO2 is better than that ZrO2 coating. Both plasma sprayings have similar abrasive wear behavior; however, the average friction coefficient is higher for alumina–titania coating. Electrochemical tests, open circuit potential monitoring and potentiodynamic polarization, were performed in simulated body conditions (Hank’s solution, 37°C). Results showed that corrosion resistance was appreciably higher for alumina–titania coating. [Copyright &y& Elsevier]

We investigate the evolution of the surface of a highly alloyed stainless steel (Sanicro 28) upon immersion in aqueous phosphoric acid solutions. For this purpose, both short- (few hours) and long-term immersion (several days) were carried out. A detailed analysis of XPS spectra allowed a distinction to be made between oxygen originating from the organic adlayer (adventitious contamination), the passive oxide layer, and adsorbed phosphate species. By estimating the fraction of oxygen due to phosphate species ( O ph ), it was shown that the O ph / P molar concentration ratio was ranging from about 2 to 3. This suggests the presence of a polyphosphate layer at the stainless steel surface, as also supported by Raman analysis, which influence the electrochemical behavior of SS in the acidic media. [ABSTRACT FROM AUTHOR]

Studying the stimuli-response of polyelectrolyte multilayers (PEMs) towards protein adsorption requires coping with the multiplicity of factors influencing interfacial processes. In this study, we report the design of a nanostructured stimuli-responsive coating based on the sequential layer-by-layer assembly of poly(N-isopropylacrylamide) block copolymers with poly (allylamine hydrochloride) and scrutinize its ability to modulate protein adsorption. The results reveal that the stimuli-response of the film towards protein adsorption under T, pH and I changes is strongly influenced by the type of buffer. This latter parameter has indeed a significant impact on the adsorbed amount of proteins, while it has only slight effect on the stimuli-response of free block copolymer, on the mechanism of PEM growth and the properties of the obtained film. In conditions favorable to protein adsorption, the use of anionic buffer leads to the adsorption of an apparent monolayer of proteins, while in zwitterionic buffer, proteins adsorb in a significantly higher amount. This trend may be explained by a more efficient charge screening of macromolecules by zwitterions which reduce the repulsion between proteins, leading to their accumulation at the interface. Finally, the length of the poly(N-isopropylacrylamide) block is shown to be another key factor impacting the amount of adsorbed proteins. The findings reported in this paper provide relevant information and allow the evaluation of stimuli-response of PEM to be carried out under optimized conditions. [ABSTRACT FROM AUTHOR]

The corrosion behaviour of Sanicro28, in industrial phosphoric acid and simplified solution of pure H 3 PO 4 containing sulphates and chlorides, is investigated during 48 h between 20 and 80 °C. Results show higher corrosion resistance in the industrial medium. Film thickness evaluated by EIS remains constant in industrial acid due to polyphosphate that promotes crystallisation of the Cr 2 O 3 inner layer. Conversely, the passive film is partially destroyed at 80 °C in simplified acid. XPS and Raman analysis show that phosphate and molybdenum are both present in the passive film and in corrosion products. The role of Ca present in the industrial acid is discussed. [ABSTRACT FROM AUTHOR]

Abstract: We report investigations on the texture, corrosion and wear behavior of ultra-fine grained (UFG) Ti–13Nb–Zr alloy, processed by equal channel angular extrusion (ECAE) technique, for biomedical applications. The microstructure obtained was characterized by X-ray line profile analysis, scanning electron microscope (SEM) and electron back scattered diffraction (EBSD). We focus on the corrosion resistance and the fretting behavior, the main considerations for such biomaterials, in simulated body fluid. To this end, potentiodynamic polarization tests were carried out to evaluate the corrosion behavior of the UFG alloy in Hanks solution at 37°C. The fretting wear behavior was carried out against bearing steel in the same conditions. The roughness of the samples was also measured to examine the effect of topography on the wear behavior of the samples. Our results showed that the ECAE process increases noticeably the performance of the alloy as orthopedic implant. Although no significant difference was observed in the fretting wear behavior, the corrosion resistance of the UFG alloy was found to be higher than the non-treated material. [Copyright &y& Elsevier]